Abstract

A review is given on several sensory systems that enable troglophile and troglobian urodele species to orient non-visually in their extreme hypogean habitat. A new sense was discovered allowing the animals to orient according to the Earth's magnetic field, which could serve as a basic and always available reference for general spatial orientation. Moreover, working with permanent magnetic field stimuli offers a very sensitive experimental method to discover the urodeles' thresholds for other sensory modalities such as light, sounds, and other stimuli, perhaps in competition or combination with the magnetic one. Proteus' audition as underwater hearing and light sensitivity due to its partly remaining sensory cells and/or skin sensitivity were studied. Excellent underwater hearing abilities had been demonstrated for Proteus with an acoustic behavioural method. The ability of sound pressure registration in Proteus is supposed to be attained by the tight anatomical junction between the ceiling of the oral cavity and the oval window. More generally, all non-visual sensory capabilities may facilitate certain behavioral strategies, compensating for missing visual orientation. Troglobians are more likely than others to own and regularly use the sensorial opportunities of a magnetic sense for spatial orientation. Compared to their epigean relatives, cave animals may have retained phylogenetically older sensorial properties, transformed or improved them, or finally acquired new ones which enabled them to successfully survive in dark habitats. Neighbor populations living on surface did not necessarily take advantage of these highly evolved sensory systems and orientation strategies of the troglobian species and may have lost them. E.g. Desmognathus ochrophaeus is partly adapted to cave life and exhibits good magnetic sensitivity, whereas, D. monticula and D. quadrimaculatus are epigean and, although living in rather dark places, did not demonstrate magnetic sensitivity when tested with our method.